Submitted to: Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/5/2014
Publication Date: 6/3/2014
Citation: Malmierca, M.G., McCormick, S.P., Cardoza, R.E., Alexander, N.J., Monte, E., Gutierrez, S. 2014. Production of trichodiene by Trichoderma harzianum alters the perception of this biocontrol strain by plants and antagonized fungi. Environmental Microbiology. 17(8):2628-2646. Interpretive Summary: Some trichothecenes, produced by fungi that infect crop plants, are toxic to plants and can be harmful to the health of humans or animals that consume food or feed prepared from infected grain. Other trichothecenes, such as those produced by the biocontrol fungus Trichoderma arundinaceum, are toxic to harmful fungal pathogens but not to plants. In this research we found that a volatile precursor of trichothecenes had some of the same activity of the trichothecene in controlling disease causing fungi. This volatile increased the natural tomato defense to infection and limited the ability of a pathogen to cause disease. This research provides scientists with tools to identify other factors that are important in biocontrol of disease-causing fungi and may aid in designing safe and effective biocontrol organisms to use against plant fungal diseases.
Technical Abstract: Trichothecenes are phytotoxic sesquiterpenoid compounds of fungal origin which can act as virulence factors in plant diseases. Harzianum A (HA) is a non-phytotoxic trichothecene produced by Trichoderma arundinaceum. The first step in the biosynthesis of HA is the conversion of farnesyl diphosphate to trichodiene (TD), a volatile organic compound (VOC), catalyzed by a sesquiterpene synthase encoded by the tri5 gene. Expression of tri5 in the biocontrol strain T. harzianum CECT 2413 resulted in production of TD in parallel with a reduction of ergosterol biosynthesis, and to an unexpected increase in the level of squalene. Transformants expressing tri5 gene induced expression of B. cinerea BOT genes and displayed low chitinase activity, although their total antagonistic potential against phytopathogenic fungi was not reduced. VOCs released by the tri5-transformant induced expression of tomato defense genes dependent of salicylic acid (SA), and TD itself strongly induced the expression of SA-responsive genes and reduced the development of lateral roots. Together, these results suggest that TD acts as a signaling VOC in the interactions of Trichoderma with plants and other microorganisms, modulating the perception of this fungus by a given environment. In addition, its ability to induce systemic defenses indicates that a complex trichothecene structure may not be necessary for inducing such responses.